The present application claims priority under 35 U.S.C. xc2xa7119 to Japanese Patent Application No. JP2002-203421. The contents of these applications are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a vehicle operation control method and vehicle operation control apparatus for controlling an actual steering angle of a driven wheel based on a steering angle of a steering wheel and vehicle velocity.
2. Description of Related Art
As a vehicle operation control apparatus including a transmission ratio changing mechanism for changing the transmission ratio by driving a motor, provided halfway of a steering transmission system which connects a steering wheel to driven wheels, a vehicle operation control apparatus 100 which comprises a steering wheel 21, a first steering shaft 22, a second steering shaft 23, an EPS actuator 24, a rod 25, a steering angle sensor 26, a vehicle velocity sensor 27, a torque sensor 28, an EPS ECU 30, a gear ratio changing mechanism 32 (transmission ratio changing mechanism), a VGRS ECU 40 and the like, as shown in FIG. 1, is available. In the meantime, such xe2x80x9ca transmission ratio changing mechanism for changing a transmission ratio by driving an electric motor, located halfway of a steering transmission system which connects the steering wheel to the driven wheelxe2x80x9d is sometimes called variable gear ratio system (referred to as VGRS, hereinafter) depending on a case.
That is, an end of the first steering shaft 22 is connected to the steering wheel 21 and an input side of the gear ratio changing mechanism 32 is connected to the other end side of this first steering shaft 22. This gear ratio changing mechanism 32 comprises a motor, a reduction gear and the like. An end side of the second steering shaft 23 is connected to this output side of the gear ration changing mechanism and an input side of the EPS actuator 24 is connected to the other end side of the second steering shaft 23. The EPS actuator 24 is an electric type powered steering system, which is capable of converting a rotary motion inputted by the second steering shaft 23 through a rack and pinion gear (not shown) to a motion in the axial direction of the rod 25 and outputting it. Further, this EPS actuator 24 generates an assist force depending on a steering condition by means of an assist motor which is controlled by the EPS ECU 30 so as to assist steering by a driver. In the meantime, this rod 25 is mounted on driven wheels FR, FL.
A rotation angle (steering angle) of the first steering shaft 22 is detected by a steering angle sensor 26 and inputted to the VGRS ECU 40 as a steering angle signal. A steering torque by the second steering shaft 23 is detected by a torque sensor 28 and inputted to the EPS ECU 30 as a torque signal. Further, a vehicle velocity is detected by a vehicle velocity sensor 27 and inputted to the EPS ECU 30 and VGRS ECU 40 as a vehicle velocity signal. Additionally, the EPS actuator 24 contains a tire angle sensor (not shown) capable of detecting a tire angle (actual steering angle) from a moving amount of rod 25.
With such a structure, ratio between input gear and output gear is changed depending on vehicle velocity at real time by means of a motor and reduction gear in the gear ratio changing mechanism 32 and VGRS ECU 40 so as to change a ratio of output angle of the second steering shaft 23 relative to the steering angle of the first steering shaft 22. The EPS actuator 24 and the EPS ECU 30 generate an assist force for assisting steering of the vehicle driver by means of an assist motor depending on vehicle driver""s steering condition and vehicle velocity detected by means of the torque sensor 28 and the vehicle velocity sensor 27.
Consequently, the steering gear ratio corresponding to the vehicle velocity can be set. For example, an output angle to a second steering shaft 23 by the gear ratio changing mechanism 32 can be set to be increased with respect to the steering angle of the steering wheel at the time of vehicle stop or traveling at a low velocity. Further, the output angle of the gear ratio changing mechanism 32 can be set to be decreased with respect to the steering angle of the steering wheel 21 at the time of traveling at a high velocity. Meanwhile, an appropriate assist force corresponding to the vehicle velocity can be generated by means of an assist motor.
For example, if a vehicle is stopped or traveling at a low velocity, the steering gear ratio by the gear ratio changing mechanism 32 is set low and an assist force is intensified by an assist motor, so that the driven wheels can be steered largely even with a light steering operation. This facilitates the steering operation of a vehicle driver. On the other hand, if the vehicle is traveling at a high velocity, the assist force by the assist motor drops and the steering ratio by the gear ratio changing mechanism 32 is set high. Consequently, the steering operation becomes heavy and even if the steering wheel 21 is turned largely, it comes that the driven wheels are steered a little. Consequently, it can be expected that vehicle control stability is further improved.
However, in such a vehicle operation control apparatus 100, a steering gear ratio is set up corresponding to a vehicle velocity by a gear ratio changing mechanism 32 controlled by the VGRS ECU 40. Thus, when a vehicle driver executes a quick steering by turning the steering wheel 21 suddenly, a follow-up delay by the control of the gear ratio changing mechanism 32 occurs. Consequently, because the steering control on the driven wheels FR, FL continues toward an object angle even after the vehicle driver terminates his steering operation, the vehicle driver is provided with a feeling of disharmony in his driving operation, thereby the steering feeling being worsened.
Thus, in order to prevent the steering feeling from being worsened due to this follow-up delay, the JP 11-208499 A has proposed a xe2x80x9cvehicle steering apparatusxe2x80x9d in which if a control deviation between an object rotation angle by a transmission ratio changing mechanism and its output angle exceeds a predetermined threshold, this control deviation is adjusted so as to block the control deviation from exceeding a predetermined threshold.
With such a structure, when the steering wheel 21 is turned back slowly at the time of its turning-back even if it is turned suddenly at the time of its additional turning, a difference in steering amount of driven wheels FR, FL occurs although the same amount steering operation is executed at the times of the additional turning and turning-back. Thus, even if a vehicle driver returns the steering wheel 21 to its neutral position, the driven wheels FR, FL are not returned to the neutral position, so that the neutral position is deviated. Consequently, the vehicle driver is supplied with a feeling of disharmony in his steering, thereby the steering feeling being worsened.
JP 2000-344121 A has proposed a xe2x80x9cvehicle steering control apparatusxe2x80x9d in which the control deviation between the object angle and output angle of the VGRS adjusted at the time of a quick steering is memorized and when the steering wheel 21 is operated, its phase is corrected gradually so that this memorized control deviation becomes zero, thereby the deviation in the neutral position being corrected. However, even with such a structure, the deviation in the neutral position just after the quick steering cannot be blocked because correction of the deviation in the phase is carried out gradually.
Accordingly, the present invention has been achieved to solve the above-described problem and an object of the present invention is to provide a vehicle operation control method and vehicle operation control apparatus capable of improving the steering feeling.
In order to achieve the above object, according to the present invention, a vehicle operation control method for controlling an actual steering angle of driven wheels based on a steering angle by a steering wheel and vehicle velocity, comprising:
a first step of obtaining a steering angle velocity based on the steering angle by the steering wheel;
a second step of obtaining the actual steering angle of the driven wheels;
a third step of controlling a variable gain based on the vehicle velocity, the steering angle, the steering angle velocity and the actual steering angle;
a fourth step of multiplying the variable gain with the steering angle; and
a fifth step of controlling the actual steering angle of the driven wheels based on a result of multiplication in the fourth step.
Further, in order to achieve the above object, according to the present invention, a vehicle operation control apparatus for controlling an actual steering angle of driven wheels based on a steering angle by a steering wheel and vehicle velocity, comprising:
a steering angle velocity obtaining means for obtaining a steering angle velocity based on the steering angle by the steering wheel;
an actual steering angle obtaining means for obtaining the actual steering angle of the driven wheels;
a variable gain control means for controlling a variable gain based on the vehicle velocity, the steering angle, the steering angle velocity and the actual steering angle;
a multiplying means for multiplying the variable gain with the steering angle; and
an actual steering angle control means for controlling the actual steering angle of the driven wheels based on a result of multiplication by the multiplying means.
According to the present invention, the variable gain controlled based on the vehicle velocity, the steering angle, the steering angle velocity and the actual steering angle is multiplied with the steering angle and the actual steering angle of the driven wheels is controlled based on a result of this multiplication. Consequently, it comes that the variable gain is controlled based on not only the vehicle velocity but also the steering angle, the steering angle velocity and the actual steering angle and thus, the gain control which depends upon not only the vehicle velocity but also the steering angle, the steering angle velocity and the actual steering angle can be executed. That is, as compared to a case where the variable gain is controlled based on only the vehicle velocity, the variable gain can be controlled based on the steering angle velocity by the steering wheel, the turning direction or the actual steering angle of the driven wheels as well. For example, it can be so set up that at the time of additional turning, the follow-up delay in the actual angle control of the driven wheels due to a quick steering is corrected and that at the time of turning-back, a deviation in the neutral position of the steering wheel is corrected. Therefore, the steering feeling can be improved.
Further, in accordance with the more preferred teaching of the present invention, the third step comprises:
a 3a step of judging which the turning direction of the steering wheel is in an additional turning direction which increases the steering angle or in a turning-back direction which decreases the steering angle, based on the steering angle and the steering angle velocity; and
a 3b step of if the turning direction of the steering wheel judged in the 3a step is the additional turning direction, selecting an additional turning time variable gain as the variable gain and if the turning direction is the turning-back direction, selecting the turning-back time variable gain as the variable gain.
Still further, in accordance with the more preferred teaching of the present invention, the variable gain control means comprises:
a turning direction judgment means for judging which the turning direction of the steering wheel is in an additional turning direction which increases the steering angle or in a turning-back direction which decreases the steering angle, based on the steering angle and the steering angle velocity; and
a variable gain selection control means for, if the turning direction of the steering wheel judged by the turning direction judgment means is the additional turning direction, selecting an additional turning time variable gain as the variable gain and if the turning direction is the turning-back direction, selecting the turning-back time variable gain as the variable gain.
In accordance with the more preferred teaching of the present invention, in controlling the variable gain based on the vehicle velocity, the steering angle, the steering angle velocity and the actual steering angle, which the turning direction of the steering wheel is additional turning direction which increases the steering angle or turning-back direction which decreases the steering angle is judged based on the steering angle and the steering angle velocity. Then, if it is judged that the turning direction of the steering wheel is the additional turning direction, an additional turning time variable gain is selected as the variable gain and if it is judged that the turning direction is the turning-back direction, the turning-back time variable gain is selected as the variable gain. Consequently, the additional turning time variable gain or the turning-back time variable gain set up individually can be selected depending on the turning direction of the steering wheel. Thus, it can be so set up that the additional turning time variable gain corrects the follow-up delay in the actual steering angle control of the driven wheels due to a quick steering and that the turning-back time variable gain corrects the deviation in the neutral position of the steering wheel. Thus, the steering feeling can be improved both at the times of the additional turning and turning-back.
In accordance with the more preferred teaching of the present invention, as for the additional turning time variable gain of the third step, the variable gain is determined based on the vehicle velocity and the steering angle velocity and as for the turning-back time variable gain of the third step, the variable gain is determined based on the steering angle and the actual steering angle.
Further, in accordance with the more preferred teaching of the present invention as for the additional turning time variable gain by the variable gain control means, that variable gain is determined based on the vehicle velocity and the steering angle velocity and as for the turning-back time variable gain by the variable gain control means, that variable gain is determined based on the steering angle and the actual steering angle.
In accordance with the more preferred teaching of the present invention, as for the additional turning time variable gain, the variable gain is determined based on the vehicle velocity and the steering angle velocity and as for the turning-back time variable gain, the variable gain is determined based on the steering angle and the actual steering angle. Consequently, because the additional turning time variable gain is determined based on not only the vehicle velocity but also the steering angle velocity, the additional turning time variable gain can be determined corresponding to the steering angle velocity attained by the steering wheel. Further, because as for the turning-back time variable gain, the variable gain is determined based on the steering angle and the actual steering angle regardless of the vehicle velocity, the turning-back time variable gain can be determined according to a ratio between the both such that the driven wheels are located at a neutral position when the steering wheel is located at the neutral position. Therefore, the steering feeling can be improved both at the time of the additional turning and turning-back.
In the meantime, the additional turning time variable gain may be determined based on a product between a first gain characteristic set up according to increase/decrease of the vehicle velocity and a second gain characteristic which decreases following an increase in the steering angle velocity. Further, as for the turning-back time variable gain, that variable gain may be determined based on a result obtained by dividing a current actual steering angle corresponding to the steering angle by the steering angle.
Consequently, because the gain is decreased by the second gain characteristic following an increase in the steering angle velocity at the time of additional turning, the additional turning time variable gain at the time of a quick steering can be decreased by the product between the first gain characteristic and the second gain characteristic. Thus, a follow-up delay of the vehicle operation control due to a quick steering at the time of the additional turning can be suppressed, thereby the steering feeling being improved. Further, because the variable gain value is determined based on a result obtained by dividing a current actual steering angle corresponding to the steering angle by the steering angle when the steering wheel is turned back, the steering wheel can be turned back by an amount corresponding to the current actual steering angle. Therefore, because the steering wheel can be located at the neutral position after it is turned back, a deviation in the neutral position can be suppressed, thereby the steering feeling being improved.